This invention relates to concrete products and structure for making the same. More particularly, the invention relates to molds for fabricating concrete slabs with stylized surface patterns.
Precast concrete slabs have been used in the building construction industry for many years. Usually, the concrete slabs are poured using production line techniques at a remote factory site and then transported to various construction sites where the slabs are used in the construction of exterior walls, floors, roofs, fireplace hearths, etc. One of the many advantages of precasting concrete slabs is the ability to place a stylized pattern onto the surface of the slab during its casting. A number of devices have been invented to facilitate the molding of such concrete slabs. For example, U.S. Pat. No. 3,954,377 discloses a vertical mold for making textured concrete panels.
When the concrete mixture is prepared water is added for two reasons: First, it is necessary for hydrolysis, a chemical reaction which occurs as the cement hardens; and second, it is necessary to put the mixture into a semi-liquid state so that it can be poured into the mold and impressed with a stylized surface pattern. If there is insufficient water in the mixture it is difficult to obtain the desired pattern detail. However, it is well known that a reduction in the amount of water in excess of the amount needed for hydrolysis increases the strength and density of the resulting concrete.
Various techniques have been developed to remove excess water from concrete which has been poured into a mold. These include the application of heat, vibration, pressure, suction, vacuum, or any combination of these, to the concrete mixture while it is in the mold before the hardening process begins. However, known techniques require the utilization of complicated and often cumbersome apparatus, such as that disclosed in U.S. Pat. No. 2,311,358 or in U.S. Pat. No. 2,798,278. Frequently they do not produce articles with precise and uniform dimensions. Often the detail of the stylized surface patterns is not of high quality.